1. Field of the Invention
The present invention relates to an imaging apparatus that obtains an image captured by an optical system having a wide angle and a large magnification chromatic aberration and distortion, and, more particularly to a technology for correcting a magnification chromatic aberration and distortion of an obtained image.
2. Description of the Related Art
Recently, demands for a wide-angle small imaging apparatus have been increasing for an application such as a back monitor of a vehicle. However, it is difficult to design a small optical system with a small magnification chromatic aberration and distortion, and performance needs to be improved in combination with image processing. In this case, coordinate transform has been conventionally performed in a subsequent stage for image data obtained by an imaging device such as a charge coupled device (CCD) and a complimentary metal oxide semiconductor (CMOS) sensor to correct the magnification chromatic aberration and distortion.
FIG. 17 is a configuration diagram of a conventional imaging apparatus of this type. In FIG. 17, an imaging device 1 is a CCD or CMOS sensor, and converts an optical image captured through an optical system having a wide angle and a large magnification chromatic aberration and distortion (not shown) into an electrical signal (image data). A counter 2 generates a coordinate value (x, y), which is a frame address, based on a clock and a horizontal/vertical synchronization signal (not shown) provided from outside. The image data is sequentially read from the imaging device 1 based on the coordinate value (x, y) of the counter 2 and sequentially written in a frame memory 3. The frame memory 3 can be a line buffer for a predetermined number of lines. Meanwhile, a coordinate transforming unit 4 inputs the coordinate value (x, y) of the counter 2 to calculate a transformed coordinate for correcting the magnification chromatic aberration and distortion according to a predetermined formula of coordinate transform, and sequentially reads the image data from the frame memory 3 by using the transformed coordinate value (x, y). Accordingly, magnification chromatic aberration-corrected and distortion-corrected image data is read from the frame memory 3.
For example, in Japanese Patent Application Laid-open No. 2006-345054 are described a method of correcting a magnification chromatic aberration and distortion simultaneously, by performing coordinate transform independently for each of RGB color components in R (red), G (green), and B (blue) signals obtained by an imaging device such as a CCD or CMOS sensor in a subsequent stage, and a method of correcting only distortion by performing coordinate transform for respective RGB color components at the same time, ignoring magnification chromatic aberration.
In the conventional technique, a large-capacity frame memory or line buffer has been required separately to realize coordinate transform for correcting the magnification chromatic aberration and distortion. Particularly when the magnification chromatic aberration and distortion are corrected simultaneously by independently performing coordinate transform for each RGB color component, a memory capable of addressing independently for each RGB color component is required, and it is necessary to use an expensive 3-port random access memory (RAM) (for example, a static RAM (SRAM)) having a 3-chip configuration or to drive a RAM in a time-sharing manner. Further, when only the distortion is corrected by performing coordinate transform commonly to the RGB color components, although a low-cost dynamic RAM (DRAM) or the like having a 1-chip configuration can be used, a memory is still required separately.
Generally, a color filter such as of a Bayer array is provided in the imaging device. In the conventional technique, after a defective pixel due to a color filter array such as the Bayer array is interpolated, the magnification chromatic aberration and distortion are corrected with respect to a signal obtained by the imaging device, and thus a large-capacity frame memory or line buffer is required separately.